How about the pitch of your saddle? Is the saddle some what level with the ground or top tube? If the nose is slightly pointed downwards, it can cause your body to be "falling" forward and then looking up the road is uncomfortable. Although some people may think that their bike looks faster or cooler with there is a large difference between the height of the saddle and the tops of the bars, unless you are long armed, this is not necessarily a comfortable position. You actually want the bars and saddle to be pretty close in height, with the saddle slightly higher than the bars but not significantly higher. Finally, one of the most fatiguing things about riding long distances on a bike is shoulder and neck pain. You head is heavy to hold up.